Planetas gigantes "super leves"

Visão artísticas dos planetas "superfofos" comparados com os planetas gigantes do Sistema Solar e a Terra. Fonte:  Foto: NASA/ESA/Hulstak/Olmsted/Player/Summers.

Recentemente foi publicado um artigo mostrando um fato bastante curioso: planetas gigantes, do tamanho semelhante ao de Júpiter, mas com a massa somente de algumas vezes a massa da Terra no sistema Kepler 51. Esse planetas possuem a densidade igual ao de um algodão doce. Uma das razões para existência desses planetas "leves" é a idade: o sistema Kepler 51 é muito jovem, tem menos que 500 milhões de anos. Esses planetas devem perder parte da atmosfera e o restante deve "condensar", no final esses planetas devem ficar do tamanho de mini Netunos.

Abstract do artigo:

The Kepler mission revealed a class of planets known as “super-puffs,” with masses only a few times larger than Earth’s but radii larger than Neptune, giving them very low mean densities. All three of the known planets orbiting the young solar-type star Kepler 51 are super-puffs. The Kepler 51 system thereby provides an opportunity for a comparative study of the structures and atmospheres of this mysterious class of planets, which may provide clues about their formation and evolution. We observed two transits each of Kepler 51b and 51d with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. Combining new WFC3 transit times with reanalyzed Kepler data and updated stellar parameters, we confirmed that all three planets have densities lower than 0.1 g $cm^{−3}$. We measured the WFC3 transmission spectra to be featureless between 1.15 and 1.63 μm, ruling out any variations greater than 0.6 scale heights (assuming a H/He-dominated atmosphere), thus showing no significant water absorption features. We interpreted the flat spectra as the result of a high-altitude aerosol layer (pressure < 3 mbar) on each planet. Adding this new result to the collection of flat spectra that have been observed for other subNeptune planets, we find support for one of the two hypotheses introduced by Crossfield & Kreidberg, that planets with cooler equilibrium temperatures have more high-altitude aerosols. We strongly disfavor their other hypothesis that the H/He mass fraction drives the appearance of large-amplitude transmission features.

Link do artigo completo aqui.